[Bug 77580] GCC memory starvation caused by flatten attribute with LTO

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=77580

--- Comment #8 from Patrick McMunn <doctorwhoguy at gmail.com> ---
(In reply to main.haarp from comment #6)
> (In reply to Patrick McMunn from comment #5)
> > Created attachment 125089 [details] [review] [review]
> > Patch to allow LTO optmization of xf86-video-intel
> > 
> 
> Nice work! This allows building with LTO on gcc-4.9. gcc-5.3.0 however fails
> to build it, throwing a bunch of these around:
> 
> /usr/include/bits/string3.h:50:1: error: inlining failed in call to
> always_inline ‘memcpy’: target specific option mismatch
> 
> 
> Also, unlike your P4, I cannot detect any measurable performance
> improvements (Intel Sandy Bridge). Unfortunate.
> 
> All tests done with xf86-video-intel from today's git.

Hmm... You shouldn't be getting that error. That's the error I was getting
before I removed the "always_inline" definitions. If the patch worked properly
for you, the compiler shouldn't be running into a "always_inline" directive.

I don't think I actually tested it with 5.3.0. I only verified that it builds
with 4.9.3, and all my tests with performance involved 6.1.0.

I did do numerous tests involving various compiler flags such as -O2, -O3,
graphite compiler flags, etc, and I found that I actually got reduced
performance with -O3 compared to -O2, and I got reduced performance with using
additional optimizations like graphite. The biggest improvement I got was with
simple -O2 and a proper -march setting.

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